Method of jet grinding and gas centrifugal classification of powders

Abstract

FIELD: powder classification.SUBSTANCE: invention relates to the field of gas-jet grinding and gas classification of bulk materials and can be used in the metallurgical, microelectronic, chemical, pharmaceutical and other industries. The method includes feeding the initial powder, mixing the flows, dispersing the powder particles, grinding, entrainment, separating the ground powder from the gas, and returning the large particles for re-grinding. The initial powder is fed from the vibratory feeder (1) through the auger (3) into the jet grinder (4), made of a lower conical and upper cylindrical parts. The powder is ground by feeding a vertical jet of gas into an accelerating tube with a collector installed along the axis of the grinder, through a nozzle (5a) in the centre of the bottom of the conical part of the grinder and two radial counter jets of gas through nozzles (5b and 5c) into the cylindrical part of the grinder above the accelerating tube. The coarse powder fraction is returned to the conical part of the grinder under the action of gravitational forces using a profiled impact device with a conical part angle of at least 45°, located above the acceleration pipe, and gas centrifugal classification of the powder is carried out using a rotor installed coaxially in the upper part of the grinder, with the speed of the vertical Uv and radial Ur jets, the volumetric gas flow rate Q and the angular velocity of rotation of the rotor Ω vary in the following ranges: Uv = 140-210 m / s; Ur = 340-450 m / s; Q = 40-100 m3 / h;Ω = 5000-20000 rpm. Additional cleaning and classification of the powder from gas is carried out using a battery of cyclones with a cartridge filter, arranged in series and connected to the outlet pipe of a jet grinder, and dried neutral gas is fed into the nozzles.EFFECT: increase in the degree of grinding of powder material, a reduction in specific energy consumption, an increase in the safety of the process, and an expansion of the class of materials to be ground.3 cl, 3 dwg, 1 tbl, 1 ex

Description

[0001] The invention relates to the field of gas-jet grinding and gas classification of bulk materials and can be used in the metallurgical, microelectronic, chemical, pharmaceutical and other industries.

[0002] Jet grinding is based on the processes of impact and abrasive interaction of particles in two-phase flows with each other and / or with an obstacle using the kinetic energy of the gas.

[0003] A known method for jet milling of powdered materials [1] utilizes an air stream supplied through a gas pipeline to an injector and an accelerator tube, capturing particles of the material being ground, which enter the grinder through a nozzle. In the accelerator tube, the particles of the material being ground acquire the required velocity and impact the grinding plate. The disintegrated particles are carried by the gas flow through guide vanes into a separator, where centrifugal force separates the ground particles into two fractions. The fine fraction is removed through the nozzle, while the coarse fraction, having reached the walls of the housing, descends into the grinding zone. The grinding fineness is adjusted by adjusting the position of the separator's guide vanes.

[0004] The disadvantages of this method are coarse grinding with high specific energy consumption, as well as the use of an air jet.

[0005] A known method implemented in a device for grinding and classifying powders [2]. The original powdery material is fed from a hopper through an ejector chamber into a grinding chamber by means of an ejection effect. Compressed air is supplied to the grinding chamber through nozzles. In the grinding chamber, counter-directional air flows and mutual collisions of particles cause the powdery material to be ground. The powder then enters the inlet of the rotor of a centrifugal separator. After separation in the centrifugal separator, the coarse fraction of the powder is separated into the grinding chamber for regrinding. The fine fraction is carried through the outlet pipe to a coarse cyclone dust separator. The highly dispersed powder material remaining in the air flow is captured in a fine cyclone and accumulated in the receiving hopper. A ceramic filter serves for final air purification.

[0006] This method has the following disadvantages: low grinding efficiency due to the low acceleration rate of the crushed particles, low material consumption, and high specific energy consumption. Furthermore, this device operates in an air environment.

[0007] The closest technical solution to the claimed invention is a method and device for crushing bulk materials [3].

[0008] The method for crushing bulk materials includes loading the material to be crushed into an additional material feed chamber, feeding an ejected gas with a pressure higher than atmospheric, feeding the ejecting gas , mixing of gas and crushed material flows, particle acceleration, particle crushing, carryover, separation of crushed material from gas, return of large particles for re-crushing.

[0009] The method chosen as a prototype is characterized by the following disadvantages: low degree of grinding of powder material due to low acceleration speed, lack of gas classification and multiple circulation movement of two-phase flow.

[0010] The technical result of the claimed invention is to increase the degree of grinding of powder material, reduce specific energy consumption, improve the safety of the technological process, and expand the class of materials to be ground.

[0011] The technical result is achieved by developing a method for jet milling and gas classification of powders. This method includes feeding the feedstock powder, mixing the streams, dispersing the powder particles, milling, entrainment, separating the milled powder from the gas, and returning the larger particles for re-milling. The feedstock powder is fed from a vibratory feeder through a screw into a jet mill consisting of a lower conical section and an upper cylindrical section.The powder is ground by feeding a vertical gas stream through a nozzle located in the center of the bottom of the conical part of the grinder into an accelerating pipe with a collector installed along the axis of the grinder, as well as two radial counter-current gas streams through nozzles into the cylindrical part of the grinder above the accelerating pipe, wherein the coarse fraction of the powder is returned to the conical part of the grinder with the help of a profiled baffle with an angle of the conical part of at least 45°, located above the accelerating pipe, and gas centrifugal classification of the powder is carried out using a rotor installed coaxially in the upper part of the grinder, while the speed of the vertical U. в and radial U р jets, gas flow rate Q, and rotor angular velocity Ω vary in the following ranges:

[0012] U в =(140÷210) m / s;

[0013] U р =(340÷450) m / s;

[0014] Q= (40 ÷ 100) m 3 / hour;

[0015] Ω = (5000 ÷ 20000) rpm.

[0016] Further cleaning and classification of the powder is carried out using a battery of cyclones and a cartridge filter, arranged in series and connected to the outlet pipe of the jet grinder, with dried neutral gas supplied to the nozzles.

[0017] The positive effect of the invention is achieved by the following factors.

[0018] 1. The screw feed of the feed powder from the vibratory feeder to the jet grinder ensures the disintegration of the powder particles and their metered feed into the conical part of the grinder, taking into account the selection of the oscillation frequency of the feeder for different powder materials and different dispersions.

[0019] 2. The conical shape of the lower part of the grinder body ensures the concentration of powder particles in the ejection zone at the entrance to the acceleration pipe.

[0020] 3. The vertical gas jet supplied through the nozzle in the center of the conical bottom of the grinder into the lower part of the dispersing pipe with the inlet manifold ensures the capture of polydisperse powder and the movement of a two-phase flow in the dispersing pipe, thereby self-grinding large powder particles.

[0021] 4. The supply of two radial counter-jet streams at the outlet of the accelerator tube provides additional jet milling based on the processes of impact and abrasive interaction of particles in two-phase flows with each other.

[0022] 5. Vertical speed range в =(140÷210) m / s, range of radial counter jet speeds U р = (340÷450) m / s and volumetric gas flow rate Q= (40 ÷ 100) m3 / hour were selected experimentally during the development of the claimed method for a wide class of powders.

[0023] 6. A profiled baffle above the accelerating tube ensures the return of coarse powder particles to the conical section of the grinder and their repeated passage through the accelerating tube. This ensures the intensity of powder grinding due to the impact interaction of particles, which improves the fineness of the spray of high-strength material powders and reduces specific energy consumption.

[0024] 7. The upper inclination angle of the conical part of the chipper is not less than 45° to prevent the powder from sticking to the chipper.

[0025] 8. Carrying out gas centrifugal classification using a rotor installed coaxially at the top of the grinder ensures the classification of powder due to the spatial separation of particles of different sizes in the field of centrifugal mass forces.

[0026] 9. The range of angular velocity of rotor rotation Ω = (5000 ÷ 20000) rpm was selected experimentally during the development of the claimed method for a wide class of powders.

[0027] 10. The use of dry neutral gas supplied to the grinder eliminates the oxidation of the particles of the powder being ground, which expands the class of materials for the powder being ground and also reduces the fire and explosion hazard of the process equipment.

[0028] The essence of the invention is explained by drawings.

[0029] Fig. 1 - General diagram of the device implementing the claimed invention, where the following are designated: vibratory feeder 1, pneumatic vibrator 2, auger 3, jet grinder 4, nozzles 5a, 5b, 5c, inlet manifold 6, acceleration pipe 7, baffle 8, rotor 9, gas valves of rotor bearings 10, electric motor 11, pressure regulator of the valve system 12, outlet pipe 13, cyclones 14a, 14b, containers of precipitated powder 15a, 15b, 15c, cartridge fine filter 16, regeneration system solenoid valves 17a, 17b, regeneration system pressure regulator 18, nitrogen compressor station 19.

[0030] Fig. 2 - Graphs of differential and integral particle size distributions for the original tungsten powder.

[0031] Fig. 3 - Graphs of differential and integral particle size distributions of ground tungsten powder.

[0032] The device for implementing the claimed method, the diagram of which is shown in Fig. 1, operates as follows.

[0033] From the vibratory feeder 1, through the auger 3, the original powder is dosed into the grinder 4. The neutral gas used for grinding and classification is fed in the form of a vertical jet through the nozzle 5a located in the center of the bottom of the conical part of the grinder 4, as well as two radial counter jets of gas through the nozzles 5b and 5c into the cylindrical part of the grinder above the acceleration pipe.

[0034] A vertical gas jet from nozzle 5a with velocities Uв=(140÷210) m / s, depending on the proposed degree of grinding and classification of the powder relative to the specified boundary particle size, is directed downwards to the inlet manifold 6 of the accelerating tube 7, capturing the polydisperse powder, and the two-phase flow continues to move along the accelerating tube 7, where self-grinding of the material occurs. At the outlet of the accelerating tube 7, the dust-gas flow is subjected to the action of two radial counter-jet nozzles 5b, 5c, moving at velocities U р=(340÷450) m / s above the acceleration pipe 7 of the cylindrical section of the grinder. A profiled impactor 8 is installed above the acceleration pipe 7, with an upper conical angle of at least 45°, where the powder is further ground. The impactor also returns the coarse powder fraction to the conical section of the grinder. This creates a recirculation movement of the dust-gas mixture, which allows for increased powder grinding to 1 µm or finer.

[0035] The baffle is designed to maximally turn and distribute the two-phase flow towards the surface of the upper level of the powder located in the grinder container, thereby reducing the concentration of the solid phase in the area of ​​​​the rotor 9, and therefore reducing the number of particles passing through it for classification.

[0036] Gas centrifugal classification of powder is carried out under the influence of centrifugal forces created by rotor 9 with an angular rotation speed of Ω = (5000 ÷ 20000) rpm, depending on the specified boundary size of particles, and located coaxially in the upper part of the grinder, driven into rotation by electric motor 11 and oppositely directed forces of aerodynamic resistance of particles of the main swirling flow coming from nozzles 5a, 5b, 5c.

[0037] As particles pass through the rotor zone, they are separated according to the particle boundary size. , large particles are larger move to the periphery of the rotor zone 9, return to the lower block of the grinder and again enter the acceleration pipe, due to the ejector process, and small particles, together with the gas flow, are directed through the pipe 13 to the cyclones 14a, 14b and the cartridge filter 16, located in series.

[0038] Cyclones 14a, 14b and cartridge filter 16 are equipped with containers for the precipitated product 15a, 15b, 15c. Cartridge filter 16 for fine cleaning, with regeneration system solenoid valves 17a, 17b and regeneration system pressure regulator 18 serve for the final separation of particles from the gas.

[0039] Implementation example

[0040] As an example of the implementation of the claimed method, we will consider the results of jet grinding and gas centrifugal classification of tungsten powder.

[0041] Figure 2 shows graphs of differential and integral particle size distributions, as well as the average particle size values ​​obtained using the Mastersizer device for the original tungsten powder.

[0042] From Fig. 2 it follows that the average volume diameter of the particles of the original tungsten powder D 43 = 12.92 µm, and the maximum diameter

[0043] D ma x = 60 µm.

[0044] Figure 3 shows graphs of differential and integral particle size distributions obtained using the Mastersizer device for ground tungsten powder under the following operating parameters:

[0045] U в = 205 m / s;

[0046] U р = 420 m / s;

[0047] Q= 80 m 3 / hour;

[0048] Ω = 10000 rpm

[0049] From Fig. 3 it follows that the average volume diameter of particles D 43 = 0.54 µm, and the maximum diameter D max = 2 µm.

[0050] When developing the claimed method, three modes of grinding tungsten powder were investigated. The parameters of these modes (Q, Ω, U р ,U в ) and the values ​​of the average volumetric D 43 and maximumD max The particle diameters are given in the Table.

[0051] The table also shows the output performance values ​​of tungsten powder particlesG ц kg / hour.

[0052] Table

[0053] № Q, m3 / h rpm U p, m / s U in, m / s D 43 μm D max μm G h kg / hour 1 60 5000 170 350 8 17 0.71 2 70 7000 190 370 5 9 0.45 3 80 10000 205 420 0.54 2 0.29

[0054] From the results shown in the table, it can be seen that a significant reduction in the average volumetric and maximum particle diameter has been achieved while simultaneously increasing the efficiency, productivity and reliability of the gas jet grinding process followed by classification of ultrafine powders less than 10 μm.

[0055] List of references:

[0056] 1. Sidenko P.M. / Grinding in the chemical industry. / / Chemistry. 1977. P. 211-213.

[0057] 2. Patent RU 2005564 IPC B07B 7 / 083. Device for grinding and classifying powders. Published 15.01.1994.

[0058] 3. Patent RU 2711252 IPC B02C 9 / 06. Method and device for crushing bulk materials. Published 01 / 15 / 2020.

Claims

1. A method for jet grinding and gas centrifugal classification of powders, including feeding the initial powder, mixing the flows, accelerating the powder particles, grinding, entrainment, separating the ground powder from the gas, returning large particles for re-grinding, characterized in that the initial powder is fed from a vibratory feeder through a screw into a jet grinder made of a lower conical and an upper cylindrical part, the powder is ground by feeding a vertical gas stream into an accelerating pipe with a collector installed along the axis of the grinder, through a nozzle in the center of the bottom of the conical part of the grinder and two radial counter jets of gas through nozzles into the cylindrical part of the grinder above the accelerating pipe, wherein the coarse fraction of the powder is returned to the conical part of the grinder under the action of gravitational forces with the help of a profiled baffle with an angle of the conical part of at least 45°, located above the accelerating pipe,and gas centrifugal classification of powder is carried out using a rotor installed coaxially in the upper part of the grinder, while the vertical speed U, в and radial U р jets, gas volumetric flow rate Q and rotor angular velocity Ω vary in the following ranges: U в = 140-210 m / s; U р = 340-450 m / s; Q = 40-100 m 3 / h; Ω = 5000-20000 rpm.

2. The method according to paragraph 1, characterized in that additional cleaning and classification of the powder from gas is carried out using a battery of cyclones with a cartridge filter, arranged in series and connected to the outlet pipe of a jet grinder.

3. The method according to paragraph 1, characterized in that dried neutral gas is fed into the nozzles.

Images